Saturday, February 19, 2011

For months, as rockfalls enlarged the lava lake at the bottom of the pit in Halema'uma'u crater, a portion of the north rim refuesd to collapse, defying gravity.

Late Monday morning, a part of the rim of the pit, which overhangs by 180 feet, gave way, roiling the surface of the lake and spreading a thin layer of ejecta as far as the Jaggar Museum.

The small explosive episodes are a reminder of the unpredictable nature of Kilauea volcano, which is engorged with increased levels of magma.

The effects of this increase in the magma supply are readily apparent, from the rising lava lake in Halema'uma'u to the crater-filling effusive lava flows at the 28-year-old Pu'u 'O'o vent.

At the rim of Halema'uma'u, a camera perched near the destroyed visitor overlook gave a clear look at both explosive events. In the first of a series of events, part of the pit gave way around 8:42 a.m., falling onto the bubbling surface of the lava lake 250 feet below. Huge boulders, the size of bathrtubs or larger, hit the surface and disintegrated into a cloud of rock ash, which then rose high into the air as a dusty brown plume. About five or six of these events were recorded.

At 11:35 a.m., a large piece of the vent wall, estimated to be about 395 feet long and up to 16 feet wide, collapsed into the lava lake. It pushed a surge of molten rock onto the far side of the lake and released trapped gases.

Since Kilauea's summit vent first opened in Halema'uma'u in March 2008, the hole has increased from 115 feet in diameter to nearly 490 feet. Falling rock on Monday expanded the width of the vent another 15 to 30 feet , and several more collapses occured before dawn Tuesday, enlarging the vent further. Click here, for more pictures and sound bites.

The next phase in the eruption: Magma could continue to rise within the vent, eventually spilling onto the crater floor in the coming months. It might intrude into one of Kilauea's two rift zones and erupt at a weak spot. The magma might intrude into the rift zone and not erupt. Or for some reason, the supply of the lava to Kiauea might decrease, resulting in no new activity.